Numerical modeling on thermoelastoplastic responses of Karamay oil sand reservoir upon steam circulation considering phase change of bitumen

Abstract

Steam assisted gravity drainage technology has been widely applied to bitumen recovery in Karamay, northwest China. Steam circulation prior to production is designed to establish the thermal inter-well communication, aiming to create a desired initial steady steam chamber. Phenomenologically, the in situ immobile extremely viscous bitumen undergoes the change from solid to fluid state due to rheological fusion, and correspondingly the pay zone displays heated fusion and cold solid regions, within which thermal and mechanical properties differ considerably. To investigate these complex geomechanical responses, the heat transfer with phase change here was treated as a heat conduction with a moving boundary, and the modified Drucker-Prager model with cap plasticity was adopted to depict the mechanical behavior of oil sands. All models here used temperature-dependent constitutive parameters. This contribution coupled heat transfer, phase change and thermoelastoplastic deformation behaviors using a finite element code. A case study on SAGD well pairs using field operation parameters was conducted, and all reservoir information concerning temperature, phase change, deformation, stress and plastic zones were predicted. Temperature, deformation and stress along some typical paths at varying circulation periods were exhibited and discussed. The evolutions of phase change interfaces and plastic zones were provided. The changes of reservoir temperature as well as bitumen fluidity have significant impacts on the geomechanics, characterized by these interesting phenomena such as a maximum reservoir uplift occurring right above injection well, a high stress interference zone with shapes of arch or ellipse, and a plastic zone related to temperature distribution. This paper provides a coupled approach for the evaluation of reservoir thermoelastoplastic responses in steam circulation process, and it can also predict deformation change in permafrost and hydrate formation where transient heat transfer occurs incorporating phase change behavior.